538 research outputs found
Yang-Mills Flow and Uniformization Theorems
We consider a parabolic-like systems of differential equations involving
geometrical quantities to examine uniformization theorems for two- and
three-dimensional closed orientable manifolds. We find that in the
two-dimensional case there is a simple gauge theoretic flow for a connection
built from a Riemannian structure, and that the convergence of the flow to the
fixed points is consistent with the Poincare Uniformization Theorem. We
construct a similar system for the three-dimensional case. Here the connection
is built from a Riemannian geometry, an SO(3) connection and two other 1-form
fields which take their values in the SO(3) algebra. The flat connections
include the eight homogeneous geometries relevant to the three-dimensional
uniformization theorem conjectured by W. Thurston. The fixed points of the flow
include, besides the flat connections (and their local deformations), non-flat
solutions of the Yang-Mills equations. These latter "instanton" configurations
may be relevant to the fact that generic 3-manifolds do not admit one of the
homogeneous geometries, but may be decomposed into "simple 3-manifolds" which
do.Comment: 21 pages, Latex, 5 Postscript figures, uses epsf.st
A Kucha\v{r} Hypertime Formalism For Cylindrically Symmetric Spacetimes With Interacting Scalar Fields
The Kucha\v{r} canonical transformation for vacuum geometrodynamics in the
presence of cylindrical symmetry is applied to a general non-vacuum case. The
resulting constraints are highly non-linear and non-local in the momenta
conjugate to the Kucha\v{r} embedding variables. However, it is demonstrated
that the constraints can be solved for these momenta and thus the dynamics of
cylindrically symmetric models can be cast in a form suitable for the
construction of a hypertime functional Schr\"odinger equation.Comment: 5 pages, LaTeX, UBCTP-93-02
Seismic tomographic imaging of the Eastern Mediterranean Mantle: Implications for terminal-stage subduction, the uplift of Anatolia, and the development of the North Anatolian Fault
The Eastern Mediterranean captures the eastwest transition from active subduction of Earth'soldest oceanic lithosphere to continental collision, making it an ideal location to study terminalstagesubduction. Asthenospheric or subductionrelated processes are the main candidates for the region's âŒ2kmuplift and Miocene volcanism; however, their relative importance is debated. To address these issues, wepresent new P and S wave relative arrivaltime tomographic models that reveal fast anomalies associatedwith an intact Aegean slab in the west, progressing to a fragmented, partially continental, Cyprean slabbelow central Anatolia. We resolve a gap between the Aegean and Cyprean slabs, and a horizontal tear in theCyprean slab below the Central Anatolian Volcanic Province. Below eastern Anatolia, the completelydetached âBitlisâ slab is characterized by fast wave speeds at âŒ500 km depth. Assuming slab sinkingrates mirror ArabiaAnatolia convergence rates, the Bitlis slab's location indicates an Oligocene (âŒ26 Ma)breakoff. Results further reveal a strong velocity contrast across the North Anatolian Fault likelyrepresenting a 40â60 km decrease in lithospheric thickness from the Precambrian lithosphere north of thefault to a thinned Anatolian lithosphere in the south. Slow uppermostmantle wave speeds below activevolcanoes in eastern Anatolia, and ratios of P to S wave relative traveltimes, indicate a thin lithosphere andmelt contributions. Positive central and eastern Anatolian residual topography requires additional supportfrom hot/buoyant asthenosphere to maintain the 1â2 km elevation in addition to an almost absentlithospheric mantle. Smallscale fast velocity structures in the shallow mantle above the Bitlis slab maytherefore be drips of Anatolian lithospheric mantle
Le champ filonien à Zn-(Pb, Cu, As, Hg) du district minier de Fedj HassÚne (Nord Ouest de la Tunisie): Minéralogie, Eléments en traces, Isotopes du Soufre et Inclusions Fluides
Le district minier de Fedj HassĂšne est situĂ© Ă proximitĂ© de la frontiĂšre algĂ©ro-tunisienne, Ă 10 Km au sud de la ville de Ghardimaou. Il regroupe plusieurs filons Ă Pb-Zn, localement accompagnĂ©s par des sulfures de Cu, d'As et d'Hg. Les rĂ©serves sont estimĂ©es Ă 370.000 t Ă 10% de Zn et 0,2% de Pb. Les minĂ©ralisations remplissent des fractures subparallĂšles Ă la faille d'Ain Kohla de direction ESEWNW et des fentes d'extension qui recoupent les calcaires marneux du Turonien moyen. Le filon principal est formĂ© par de la sphalĂ©rite massive brune et accessoirement par de la galĂšne et de la barytine. Le minerai peut se prĂ©senter sous forme massive ou sous la forme de ciment de brĂšche. L'association minĂ©rale est composĂ©e par de la sphalĂ©rite, galĂšne, chalcopyrite, pyrite et orpiment. La gangue est formĂ©e par de la calcite massive et localement par de la barytine et du quartz. L'analyse des Ă©lĂ©ments en trace dans la sphalĂ©rite rĂ©vĂšle des teneurs en poids de 0,84% Fe, 0,14% Cd et 0,02% Mn. L'Ă©tude des inclusions fluides dans la calcite et la sphalĂ©rite montre l'existence d'un fluide caractĂ©risĂ© par une salinitĂ© de l'ordre de 23% poids Ă©quiv. NaCl Ă tempĂ©rature dĂ©croissante lors de la mise en place des minĂ©ralisations (194 °C lors du dĂ©pĂŽt de la calcite et 133 °C lors du dĂ©pĂŽt de la sphalĂ©rite). Ce fluide est caractĂ©risĂ© par une densitĂ© comprise entre 1,00 g/cm3 et 1,11 g/cm3 avec une pression de piĂ©geage estimĂ©e de 200 bars. La prĂ©cipitation des sulfures parait ĂȘtre contrĂŽlĂ©e par une chute de la tempĂ©rature. Les mesures des isotopes du soufre dans la sphalĂ©rite donnent des valeurs de ÎŽ34S toutes positives et variant dans une gamme trĂšs restreinte comprise entre + 4,6â° et 6,4â° VCDT (moyenne=5,6â°). Ces valeurs indiquent une origine commune du soufre rĂ©duit qui est formĂ© par les processus de rĂ© duction thermique de sulfates. La source des sulfates admet les Ă©vaporites triasiques de la rĂ©gion comme reservoir potentiel. Les Ă©tudes gĂ©ologiques et minĂ©ralogiques couplĂ©es Ă la microthermomĂ©trie des inclusions fluides et la gĂ©ochimie des Ă©lĂ©ments en traces et des isotopes du soufre permettent de classer le gisement filonien de Fedj HassĂšne dans le groupe des gisements polymĂ©talliques (Pb-Zn-As, Hg) typiques de la zone des nappes de la Tunisie du Nord et de l'AlgĂ©rie nord-orientale
Surface Subsidence Over Deep Solution Mined Storage Cavern Field
Ten years observation by GDF on Tersanne solution-mined gas storage field, offers the opportunity for a mechanical interpretation of the surface subsidence. According to the geological context, the rockmass was modellised by a two-layered medium with highly contrasted mechanical behavior: a soft elastic clay cover, and a viscous salt mass. Given the field uncertainties, mostly related to the cover layer, and the three- dimensional nature of the problem, indirect methods were used to obtain bounds for the surface subsidence evolution and a parametric study was performed. Comparison with data of the field allows to determine likely rock mass parameters, put forward some typical mechanical response, and give some insight on the trends of the subsidence phenomena
Investigation of plastic deformation heterogeneities in duplex steel by EBSD
An EBSD analysis of a duplex steel (austeno-ferritic) deformed in tension up to fracture is presented. The main purpose of the paper is to describe, qualitatively and quantitatively, the differences in the behavior of the two phases during plastic deformation. In order to do so, several topological maps are measured on the deformed state using the electron backscatter diffraction technique. Distributions of grain size, misorientation, image quality factor and texture are then analyzed in detail.International audienceAn EBSD analysis of a duplex steel (austeno-ferritic) deformed in tension up to fracture is presented. The main purpose of the paper is to describe, qualitatively and quantitatively, the differences in the behavior of the two phases during plastic deformation. In order to do so, several topological maps are measured on the deformed state using the electron backscatter diffraction technique. Distributions of grain size, misorientation, image quality factor and texture are then analyzed in detail
Somewhere in Europe (1947): locating Hungary within a shifting geopolitical landscape
Somewhere in Europe/Valahol EurĂłpĂĄban (RadvĂĄnyi, 1947) was one of the first films made in Hungary after 1945. Financed by the Hungarian Communist Party (MKP), it loudly proclaimed a broad European pertinence in an effort to privilege the universal narrative of childhoods disrupted by the war over narrowly national political concerns. The filmâs story of a gang of half-starved children battling for survival in a bombed-out Central European landscape places it squarely within a transnational post-war film-making tradition. Similarities with both Italian neorealism and Soviet socialist realist cinema indicate a shared European experience of the war, but is also attributable to the international training and experience of the filmâs personnel. The director RadvĂĄnyi had worked in the Italian industry, while the scriptwriter was the well-known film theorist BĂ©la BalĂĄzs, who had worked in Weimar Germany and Soviet Russia. This article argues that in spite of its ostensible commitment to a communist and humanist ideology, the film gives an insight into the Hungarian national obsession with territorial integrity. Hungaryâs participation in World War II on the side of the Axis, and its position as a defeated nation under Allied occupation, are seen to complicate the film text. This article contends that in spite its transnational flavour, the filmâs focus on lost children wandering a borderless Europe suggests a preoccupation with the countryâs uncertain position within a shifting geopolitical landscape. In turn, the filmâs official reading by NemeskĂŒrty shows an eagerness to accept the filmâs representation of Hungary as a blameless victim of the war, and gives evidence of a need to insert a (false) break between the countryâs wartime past as a member of the Axis, and the countryâs 1968 present as a member of the Communist world order
To the North Coast of Devon: Collaborative Navigation While Exploring Unfamiliar Terrain
Navigation-knowing where one is and finding a safe route-is a fundamental aspect of all exploration. In unfamiliar terrain, one may use maps and instruments such as a compass or binoculars to assist, and people often collaborate in finding their way. This paper analyzes a group of people driving a humvee from a base camp to the north coast of Devon Island in the High Canadian Arctic. A complete audio recording and video during most stops allows a quantitative and semantic analysis of the conversations when the team stopped to take bearings and replan a route. Over a period of 2 hours, the humvee stopped 20 times, with an average duration of 3.15 min/pause and 3.85 min moving forward. The team failed to reach its goal due to difficult terrain causing mechanical problems. The analysis attempts to explain these facts by considering a variety of complicating factors, especially the navigation problem of relating maps and the world to locate the humvee and to plan a route. The analysis reveals patterns in topic structure and turn-taking, supporting the view that the collaboration was efficient, but the tools and information were inadequate for the task. This work is relevant for planning and training for planetary surface missions, as well as developing computer systems that could aid navigation
Deformation heterogeneity study of a 6061-T6 aluminum alloy processed by equal channel angular pressing
Among the severe plastic deformation techniques, the equal channel angular pressing
(ECAP) has drastically improved the mechanical properties of the processed alloys. However,
information regarding friction phenomenon, which modifies the deformation at the surface and the
heterogeneity microstrain state produced by the process itself, is still scarce. In the present work, the
deformation heterogeneity and the friction effect, at the surface in the bulk material of the 6061-T6
aluminum alloy processed by ECAP, is presented and discussed. The residual stress (RS)
measurements were performed by means of X-Ray diffraction. By means of synchrotron diffraction,
volumetric sections of the ECAPed samples were characterized. Finite element analysis showed a
good agreement with the experimentally obtained residual stress and microhardness mapping
results. The study also showed that the highest deformation zones were located at the outer parts of
the deformed samples (top and bottom), while the inner zone showed strain oscillations of up to
49±2 MPa.Peer ReviewedPostprint (author's final draft
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